Lightbox Captions from Collection

I set up a set of linked lightboxes from a collection of project images, and I want to add the caption information to the collection. When the lightbox not tied to a collection, there is an option to add captions. When sourcing the media from a collection, the option for caption is gone.

Is there a good way to include captions as part of the collection information?

Here is my site Read-Only: LINK
(how to share your site Read-Only link)